Lighting devices that include a conversion coating conveniently allow the conversion of light from a source light source into a light of a different wavelength range. Often, such conversion coatings are created by using a phosphorous coating. These wavelength conversion coatings may sometimes applied to lenses located in line with the light projected from a light source. In some instances the conversion coating may be applied to the light source itself. A number of disclosed inventions exist that describe lighting devices that utilize a conversion coating to convert light with a source wavelength range into light converted wavelength range.
Color-mixing, tunable white lighting devices are traditionally controlled via PWM (pulse width modulation). PWM is a common technique for controlling power to electrical devices, which operates by quickly switching power between an “on” state and “off” state during each period. The period is the time between each pulse, similar to a clock rate. The ratio of the pulse period occupying the “on” state versus the “off” state defines the duty cycle. As the PWM varies the duration that the switch is kept at the “on” state, the PWM is able to vary the average power to the load device. PWM switching can be beneficial from an efficiency perspective, since it has low power loss when the switches are in the “off” state.
For lighting devices, the frequency of pulses in the PWM circuit must be sufficiently fast enough such that the human eye cannot perceive the strobe effect. To have an increasingly high pulse frequency, the period must become increasingly short. The intensity of each individual color may be controlled via variations in the duty cycle of each pulse period. With light sources that are slow to react, such as incandescent light bulbs, a relatively low pulse frequency may be required. Conversely, PWM circuits that may be used to control a perceived intensity of light emitting semiconductors must be operable at considerably higher frequencies, or otherwise risk producing visual flicker.
To achieve color mixing, a PWM circuit should generally be able to control the duty cycle on all colors intended to be mixed. Typically, any color can be created through the use of a red, green, and blue color source. With a color mixing system based on PWM circuits, the system may adjust the duty cycle for each primary color by combining the adjusted primary colors to display the desired color. The primary colors are normally combined via a lens.
Micro-electro-mechanical systems (MEMS) use a configuration different from PWM to control the intensity of light. In MEMS, the light from each light source is preferably directed to an array of microscopic mirrors, which reflect the light in different directions. Typically, a MEMS “on” state includes reflecting the light into a lens, wherein the light may be combined with light of other colors. Traditionally, multiple light sources are combined in MEMS to create a desired output color, including, for example, a red source, a green source, and a blue source.
U.S. Published Patent Application No. 2010/0046234 to Abu-Ageel discloses the use of wavelength conversion layers which include different types or amounts of phosphor. The Abu-Ageel '234 application gives an example of a wavelength conversion layer that may include a blend of red, green, and blue phosphors. These phosphors are excited by the light source and emit a light at a different wavelength range. The red, green and blue light generated by the conversion layers is then combined to form a white light. The Abu-Ageel '234 application also discloses the use of a blue light source, wherein the direct blue light is combined with a phosphor converted red and green light to create a white light. Furthermore, the Abu-Ageel '234 application specifically cites the use of micro-electro-mechanical systems (MEMS) and optical lenses which are used to focus a beam of light emitted by a source. A deflector can be used to scan a light beam between two or more types of wavelength conversion materials.
U.S. Published Patent Application No. 2010/0321641 to Van Der Lubbe discloses utilizing a one-colored light source, and converting fractions of that light into other colors. The Van Der Lubbe '641 application also discloses using phosphors arranged in a first and second set of pixels for a color converting optical element.
U.S. Pat. No. 7,832,878 to Brukilacchio et al., discloses phosphors or other wavelength converting elements that can be employed over an LED die to result in wavelengths and spectral bandwidths not readily available from a standard LED die. The Brukilacchio et al. '878 patent additionally discloses the use of a digital micromirror device (DMD) projection system in combination with a rotating color wheel.
U.S. Published Patent Application No. 2010/0302464 to Raring et al. discloses the use of a phosphor coating on an optical member to create a laser beam of a desired color by using a phosphor material to alter the light generated by LEDs and/or laser diodes. These colored laser beams may then be emitted to a DMD from an optical member.
There exists a need for a lighting device that provides an ability to receive a light emitted from a light source in one wavelength range and redirect the light in a desired output direction in another wavelength range. There further exists a need for a lighting device that combines conversion and redirection of the light emitted from a light source in one operation.